Dynamoelectric machines typically employ a stator core comprised of stacked laminations of magnetic material forming a generally annular assembly. An array of axially extending circumferentially spaced slots are formed through the radial inner surface of the annular assembly and armature windings are disposed in the slots. A rotor is coaxially arranged within the stator core and contains field windings typically excited from an external source to produce a magnetic field rotating at the same speed as the rotor. With the foregoing arrangement, it will be appreciated that electrical output is generated from the armature windings.
In typical stator core arrangements, the armature windings are maintained in the axially extending stator core slots by wedges axially disposed in dovetail grooves along or near the radial inner ends of the stator core. The wedges impose radial forces on the armature windings for resisting magnetic and electrically induced radial forces on the windings. In order to prevent excessive heat build-up in the ends of the stator core during operation, it is common practice to taper the ends of the stator core in a radially outer direction. This outward taper intersects the dovetails in the stator slots such that the armature windings extend from the ends of the slots to comprise the end turns without radial structural support.
More particularly, the armature windings of generators operate under continuous strain of electromagnetic forces that must be completely contained to prevent high voltage armature winding insulation damage. Insulation damage is also exacerbated by relative movement of the elements, e.g., the armature windings and stator core. For example, the core end geometry which reduces core heating also leaves the armature windings extending from the stator core unsupported at the ends of the slots. Seal oil leakage, if present, also reduces restraining friction forces applied by side ripple springs. It is also possible that static residual forces exerted by the end windings may displace the armature windings off the core slot bottom, either initially or over time in service, allowing radially outwardly directed electromagnetic forces to initiate armature winding vibration. Radial clearance may also develop over a long period of service due to aging of materials. Once clearance is developed and vibration begins, damage to armature winding insulation can accelerate quickly, particularly in the presence of oil contamination, to a point where electrical failure can occur.
A similar problem exists with respect to P-bar excitation systems, for example, disclosed in U.S. Pat. No. 4,584,497 of common assignee herewith. The P-bar windings extending from the radially innermost dovetail of the dual dovetail system disclosed in that patent are cantilevered and provided with a beam support between the radially inner dovetail and yokes supported on end space blocks of the stator core. In that arrangement, the beam is supported at opposite ends by the radially inner dovetail and the yoke to provide structural support for the P-bar windings and the underlying armature bars within that length. That patent is concerned only with P-bar windings and beam supports therefor. It has been found, however, desirable to not only provide support for the armature windings but also to provide outward radial biasing forces on the armature windings which are unsupported outboard of the stator core dovetails.